Translation initiation factor 5A (eIF-5A) is the only protein which has the modified amino acid, hypusine (spermidine addition into the lysine residue) in nature. The modification of this lysine residue, which is located in the center of a very well conserved sequence region, into hypusine, is known to be very essential for the proliferation of the cell. For these reasons, eIF5a and its modification enzyme, deoxyhypusine synthases, are considered as the target proteins for the development of an antiproliferation drug. A recent study shows that eIF-5A acts as the cofactor of human immunodeficiency virus type-1 (HIV-1) Rev trans-activator protein.